Tags: python crypto xor
Rating:
## Tile Mate
**Category:** Crypto **Points:** 100
### Solution
By looking at encryptor.py, we know that:
- key is 5 characters (10 hex)
- flag starts with ```flag{```, so we can find key by bruting over first 10 hex values of encrypted in the file.
- after finding the key, we should find next values of flag, one by one simply by bruting over printable characters (It's a simple for over printable ascii's)
- Remember flag values should contain lower values.
Here is the solution:
```python
#!/usr/bin/env python2
import string, itertools
from itertools import cycle as scooter
from hashlib import sha384
# We know this is first 5 characters of flag.
flag = "flag{"
characters = '0123456789abcdef'
encrypted = open('ci.pher.text','rb').read()
def iter_all_strings():
length = 2
while True:
for s in itertools.product(characters, repeat=length):
yield "".join(s)
return
def drive(Helmet, Petrol):
return ''.join(chr(ord(David)^ord(Toni)) for David,Toni in zip(Helmet,scooter(Petrol)))
def enc(key, flag):
f = lambda x: sha384(x).digest()[(ord(x)+7)%48]
encrypted = drive(map(f,flag),key.decode('hex')).encode('hex')
return encrypted
# Finding key
key = ''
for i in range(5):
for s in iter_all_strings():
if enc(key+s, flag)[:(i*2)+2] == encrypted[:(i*2)+2]:
key += s
break
print("key is: {}".format(key))
# Now finding the flag
flag = ""
characters = string.printable
for i in range(len(encrypted)/2+1):
enc_tmp = encrypted[:i*2]
for j in characters:
if enc(key, flag+j.lower()) == enc_tmp:
flag += j.lower()
print("flag is: {}".format(flag.lower()))
```
